Section 8.3: The Dissolving Process
Tutorial 1 Practice, page 384
1. (a) CaCl2(s) → Ca2+(aq) + 2 Cl–(aq)
(b) NH4NO2(s) → NH4+ (aq) + NO2–(aq)
(c) Fe(OH)3(s) → Fe3+(aq) + 3 OH–(aq)
(d) Al2(SO4)3(s) → 2Al3+(aq) + 3 SO42–(aq)
Mini Investigation: Exploring Selective Solubility, page 387
A. The brown layer in the test tube suggests that dissolved iodine was produced during the
experiment.
B. The compounds in mineral oil must be non-polar because after mixing with water, the oil and
water separated. When Lugol’s solution was added, only the water mixed with the polar Lugol’s
solution, creating the brown layer, while the oil layer remained on top of the brown layer. If the
compounds in the oil were polar, the oil molecules would have been attracted to the polar water
molecules and to the molecules of Lugol’s solution, and a solution would have been created.
C. In Lugol’s solution, iodine ions are in the form of I3–, which are negatively charged. These
negatively charged ions are attracted to the positive ends of polar water molecules, to form a
solution. The oil molecules have no polarity, so no attraction to water molecules can occur.
Therefore, the less the molecular polarity of a solvent, the less the solubility of iodine (as I3–) in
that solvent.
Research This: The Search for Greener Solvents, page 388
A. Answers may vary. Sample answer: Another application of green solvents is in oil refining.
The advantages of using green solvents over traditional solvents include reducing the cost of the
refining process, minimizing waste, and minimizing the effect on the environment.
B. Answers may vary. Students’ brochures should include information about how the green
solvent works, its advantages, and its applications.
Section 8.3 Questions, page 389
1. (a) Since DDT was detected in the fatty tissues of Arctic mammals, DDT is a non-polar
substance.
(b) DDT is not soluble in water, which is polar, but is soluble in hexane, which is non-polar.
2. The attractions between solute and solvent must be great enough to overcome the attractions
between solute–solute and solvent–solvent for a solute to dissolve in a solvent.
3. Water is capable of dissolving sodium chloride because water is polar. As water molecules
approach a crystal of sodium chloride, they re-orient themselves so that the negative end of the
molecule is attracted to the positively charged sodium ion and the positive end of the molecule is
attracted to the negatively charged chloride ion. Sodium chloride will not dissolve in hexane
because hexane is a non-polar molecule.
4. Water is sometimes described as “the universal solvent” because of its ability to dissolve most
compounds. However, there are many substances that do not dissolve in water, including
hydrocarbons. For that reason, water cannot be called “the universal solvent.”
5. Hydration is a necessary part of dissolving because it helps stabilize the ions in the solution,
which prevents them from attracting each other.
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Chapter 8: Water and Solutions
8.3-1
6. (a) Ca(NO3)2(s) → Ca2+(aq) + 2 NO3–(aq)
(b) KClO4(s) → K+(aq) + ClO4–(aq)
(c) (NH4)2CO3(s) → 2 NH4+(aq) + CO32–(aq)
(d) Fe2(SO3)3(s) → 2 Fe3+(aq) + 3 SO32–(aq)
7. Liquids that mix with each other are miscible. For example, ethanol and water are miscible.
Liquids that do not mix with each other are immiscible, such as oil and water in salad dressings.
8. The expression “like dissolves like” means that solutes dissolve in solvents of similar polarity.
Therefore, polar solutes dissolve in polar solvents and non-polar solutes dissolve in non-polar
solvents.
9. (a) Methanol, CH3OH, is a very polar alcohol that contains one O–H bond. This means that it
is more soluble in water than CH3OCH3.
(b) Sodium carbonate, Na2CO3, is more soluble in water than carbon dioxide, CO2 because it is
an ionic compound.
10. Methanol is more miscible with water than dichloromethane because hydrogen bonds can
form between the methanol and water molecules. Dichloromethane cannot form hydrogen bonds
with water molecules and is immiscible with water.
11. The iodine would dissolve in the corn oil to produce a purple solution. Because water and
corn oil form an immiscible mixture, the water would sit at the bottom of the test tube. The
purple solution of iodine and corn oil would sit on top of the water.
12. Lipstick is made of oils and waxes. Petroleum jelly is also made of oil. Since “like dissolves
like,” petroleum jelly will dissolve lipstick. Water does not work on lipstick because it is does
not mix with oil. Hairspray is made of polymers and solvents so it too dissolves lipstick.
13. (a) Based on these data, the factor that affects the solubility of alcohols in water is the
number of carbon chains. Alcohols with three carbon chains or less are miscible. As the number
of carbon chains increases above three, the solubility decreases.
(b) Based on the data in Table 1, the solubility of 1-octanol with 8 carbon chains would be much
less than that of 1-hexanol (6 carbon chains). Because of the large change with each carbon chain,
the solubility of 1-octanol would be very close to zero. This would be completely immiscible.
(c) The data in Table 1 can be analyzed by fitting a curve to the data or by taking the ratio of each
change in solubility with each carbon chain. The ratio of 1-butanol to 1-pentanol is 2.9. The ratio
of 1-hexanol to 1-pentanol is 4.5. From these ratios, the effect of the next carbon chain can be
estimated as approximately 7, which would result in a solubility of approximately 0.09 for
1-heptanol (7 carbon chains). The ratio for 1-octanol to 1-heptanol would be approximately 10,
which would result in a solubility of approximately 0.009. This is very close to zero and is
practically immiscible.
14. The cleaning action of soaps and detergents is an application of “like dissolves like.” Soaps
contain a long hydrophobic hydrocarbon tail and a hydrophilic head. The non-polar hydrophobic
tails are attracted to the grease and oils in the dirt while the hydrophilic heads remain surrounded
by the water molecules to which they are attracted. As the water molecules move during the
agitation of the washing machine, they pull the detergent ions along. This helps dislodge the
grease from the surface. In the water, the grease becomes coated with more detergent ions.
15. It is easier to overdose on vitamin A because it is a fat-soluble vitamin. This means that the
vitamin dissolves and remains stored in the fatty tissues. Vitamin C, which is water soluble,
dissolves in the fluids in the body and is excreted.
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Chapter 8: Water and Solutions
8.3-2
16. Persistent organic pollutants (POPs) are organic compounds that are not soluble in water.
PCBs (polychlorinated biphenyls), DDT, and dioxins are POPs. PCBs are used in electrical
equipment and added to paints and asphalt. DDT is used to control insects. Dioxins are produced
during industrial processes. POPs are considered to be toxic, and are linked to reproductive
failure and deformities in fish and wildlife.
POPs are often found in locations far from where they were originally used. This is
because POPs are semi-volatile, which means they can travel long distances through the
atmosphere before being deposited. In warm temperatures, POPs will evaporate into the air.
Winds move the air containing the POPs to colder places where the cold temperatures cause the
POPs to condense. Since POPs are not soluble, they can also accumulate in the fatty tissues of
animals and build up in the food chain. POPs can persist for years in the environment.
17. Although Canada banned the use of DDT over 20 years ago, DDT is still used in some
countries to control mosquitoes that carry malaria. DDT continues to appear in the environment,
especially in the Arctic. It is carried over long distances through the atmosphere and by
migratory birds. While DDT is considered to be moderately toxic to humans, it can cause nausea,
irritation to the eyes, nose, and throat, and increased liver enzyme activity in people exposed to
low-to-moderate levels of DDT. Exposure to high levels of DDT can cause tremors and
convulsions. Rarely does exposure to DDT cause death. Studies of the effects of DDT on test
animals have shown that DDT can cause sterility and birth defects, and is toxic to fish. Because
many Inuit hunt for their food, DDT, which accumulates in the fatty tissues of animals, can be
passed along to humans.
Inuit women have nine times higher levels of DDT in their breast milk than women in the
south. The discrepancy is related to diet. A scientist with the World Wildlife Fund Canada has
reported that hunters have seen abnormalities in harvested animals, including polar bears with
less fat and hairless seals. The suspicion is that POPs, including DDT, may be a factor in these
abnormalities. Environment Canada is working under the United Nations Environment Program
to develop a treaty that would force all countries to stop producing POPs, including DDT.
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Chapter 8: Water and Solutions
8.3-3